The primary motivation for producing water onboard an automotive vehicle is to use such water for electrolytic generation of hydrogen gas which, during a startup, can be fed into the intake of an automotive internal combustion engine (ICE) to reduce engine wear and/or into an engine exhaust system to reduce pollutants.
There are several problems that must be overcome during the start-up of a cold ICE. First, atomized or vaporous fuel in the air/fuel mixture introduced into the engine cylinders tends to condense onto the cold engine components, such as cylinder walls and the air intake rail. The potential for fuel condensation on cylinder walls is especially significant in compression ignition engines such as diesel engines. Condensed hydrocarbon fuels on engine cylinder walls may act as solvents that wash away desirable lubricant films resulting in excessive mechanical wear from reciprocating piston rings in sliding contact with the engine cylinder walls. The condensed mixture of fuel and lubricant is capable of passing the piston rings, entering the crankcase and contaminating the engine's lubrication reservoir resulting in a loss of overall lubricant effectiveness and a further increase in mechanical wear, even during normal operation. Second, the condensation of atomized or vaporous fuels onto cold engine cylinder walls results in poor engine performance and delayed engine availability during and immediately after cold engine start-up. ICE availability is diminished during cold engine start-up due to poor lubricant properties at low temperatures, non-uniform fuel distribution and improper air/fuel mixtures. Third, if the vehicle is equipped with a catalytic converter increased levels of unwanted pollutants are emitted from the tailpipe for a period of about one to three minutes after cold engine start-up because that is the amount of time normally needed for the ICE exhaust gases to heat the catalytic converter in the exhaust system to an efficient operating temperature.
The undesirable levels of pollutants released during and immediately after cold ICE start-up present a problem of increasing importance. In order to meet increasingly strict governmental engine emission standards, a catalytic converter is usually located in the exhaust stream of the engine. The conventional method of heating the catalytic converter to its efficient operating temperature is to heat the catalyst by passing high temperature exhaust gases from the ICE through the catalyst. This exhaust gas heating, in conjunction with the exothermic nature of the oxidation reactions occurring at the catalyst, will usually bring the catalyst to an efficient operating temperature, or “light-off” temperature, in one to three minutes. However, until the catalyst light-off temperature is reached, the ICE exhaust gasses pass through the catalytic converter relatively unchanged, and unacceptably high levels of pollutants such as carbon monoxide, hydrocarbons and nitrogen oxides are released into the atmosphere. According to some estimates, over 80% of the unacceptable emissions or pollutants are generated by ICE equipped with catalytic converter occur during cold start operations.
Prior art discloses several methods for overcoming these challenges. In one method gaseous hydrogen is added into the fuel mixture before combustion. In particular, Andrews et al. in U.S. Pat. No. 6,427,639 (Andrews 1) discloses a method for injecting gaseous hydrogen into ICE intake to preheat the intake gases and reduce engine wear. Murphy et al. in U.S. Pat. No. 6,122,909 discloses an apparatus for delivering hydrogen gas into ICE intake. When mixed and combusted with the hydrocarbon fuel, the gaseous hydrogen enhances the flame velocity and permits the engine to operate with leaner fuel mixtures. Thus, hydrogen has a catalytic effect causing a more complete bum of the existing fuel and yields a reduction in exhaust emissions. Apparatus disclosed by said Murphy can also inject hydrogen into ICE exhaust catalyst bed to condition NOx reducing catalyst and reduce emissions. Benninger et al. in U.S. Pat. No. 6,810,657 teaches an apparatus and a method for post treatment of ICE exhaust gases by addition of hydrogen to reduce pollutants. Breuer et al. in U.S. Pat. No. 6,871,491 discloses an emission control device using hydrogen gas to convert an automotive fluid into at least partially hydrogen-containing fuel.
Due to the advantages of using hydrogen for reducing ICE exhaust emissions and engine wear during cold startup, a number of attempts have been made to incorporate a hydrogen gas supply system with automotive vehicles. However, providing hydrogen gas as a separate fuel at automotive service stations is impractical because hydrogen distribution infrastructure for automotive use is non-existent. In addition, transport and storage of large quantities of hydrogen represent a very significant safety hazard.
To overcome this lack of hydrogen gas availability at automotive service stations, proposals have been made to produce hydrogen gas directly on board an automotive vehicle by electrolysis of water. It is well known in the art that liquid water can be dissociated into hydrogen and oxygen gases in an electrolytic cell. Electrolytic cells suitable for generation of hydrogen on-board automotive vehicles have been disclosed in prior art, for example by Andrews et al. in U.S. Pat. No. 6,698,389 (Andrews 2) and Zagaja et al. in U.S. Pat. No's. 6,857,397 and 6,659,049. To sustain appropriate hydrogen production rates requires a reliable source of liquid water. It has been earlier recognized that ICE exhaust gases contain a significant amount of water vapor which originates primarily from combustion of hydrocarbon fuel. In particular, under typical operating conditions ICE exhaust gas stream contains approximately 12% CO2, 16% H2O and 72% of other (mostly nitrogen and inert) gases by volume. Since the ICE exhaust gases are very hot (typically over 300 degrees Centigrade), all of the water contained therein is in the form of vapor. In particular, at sea level (760 Torr total ambient pressure) the partial pressure of water vapor in the ICE gases is about 118 Torr, which translates to a dew point of 55 degrees Centigrade (131 degrees Fahrenheit). At higher elevations the partial pressure of water in ICE exhaust is significantly reduced. For example, in Denver, Colo. with elevation approximately 6,500 feet (1,983 meters), the total atmospheric pressure is only about 600 Torr and the partial pressure of water in ICE exhaust is about 96 Torr, which translates to a dew point of 51 degrees Centigrade (124 degrees Fahrenheit).
To illustrate the potential of ICE exhaust gases as a source of water one may consider an automotive vehicle with an ICE moving at 100 kilometers per hour (65 miles per hour) and consuming 1.5 grams of fuel per second. Combustion of fuel at this rate would generate about 2.1 grams of water vapor per second which translates to about 7.7 kilograms of water per hour. Benz et al. in U.S. Pat. No. 5,658,449 estimates that to support hydrogen production, water should be supplied to an electrolytic cell at a rate of about 35 grams per hour. It is evident that hydrogen production needs on-board the automotive vehicle could be comfortably met by converting only a small fraction (about 0.5%) of the total available water content in ICE exhaust into liquid water.
It is well known that water condensate forms when gases containing water vapor are cooled to below the dew point. Since ICE exhaust gases passing through an automotive exhaust system are rather hot, they must undergo a very significant cooling before precipitation of liquid water is induced. Andrews et al. in U.S. Pat. No. 6,804,949 (Andrews 3) discloses a method for production of water from ICE exhaust gases wherein at least a portion of the exhaust gases at near ambient pressure is cooled to below its dew point to form liquid water condensate. Andrews estimates that at typical atmospheric conditions the dew point of ICE exhaust gases (at ambient pressure) is about 55 degrees Centigrade (131 degrees Fahrenheit).
Said Andrews 3 discloses three methods for cooling ICE exhaust gases to below dew point: 1) cooling by ambient air, 2) cooling by ICE coolant, and 3) cooling by a heat pump. The first method wherein ICE exhaust gases are cooled to below a dew point by rejecting heat to ambient air is rather ineffective on hot days when the ambient air temperature approaches the dew point of ICE exhaust gas. For example, an ambient air temperature around 40 degrees Centigrade (104 degrees Fahrenheit) is only 15 degrees Centigrade below the expected 55 degrees Centigrade dew point of ICE exhaust. It should be noted that mid-day temperatures around 40 degrees Centigrade and higher are common in many parts of the United States during the Summer. Temperature difference of only 15 degrees Centigrade between ambient conditions and the dew point does not allow for efficient heat transfer and severely limits extraction of water from ICE exhaust gases. In addition, temperatures of automotive components in proximity of the ICE (namely in the ICE compartment) and the exhaust system usually greatly exceed the temperature of ambient air. This also applies to vehicle components exposed to the sun. Consequently, cooling of ICE exhaust gases at near ambient pressure to below a dew point using ambient air is only viable in cool weather conditions.
The second method disclosed by Andrews 3 wherein ICE exhaust gases are cooled by ICE coolant is only effective when the coolant is relatively cold as it may be expected during startup especially in cool ambient conditions. However, within a few minutes of startup, the ICE warms up to its operating temperature, which results in typical coolant temperatures around 100 degrees Centigrade (212 degrees Fahrenheit). Since ICE coolant at its normal operating temperature is not capable to cool ICE exhaust gases to below the dew point of 55 degrees Centigrade, this method is effective only during the brief period of ICE startup.
The third method disclosed by Andrews 3 wherein ICE exhaust gases are cooled by a vapor-compression heat pump such as an automotive air-conditioning system can be very effective. Since an evaporator in automotive air-condition system often can reach temperatures as low as 5 degrees Centigrade a large fraction of the water content in ICE exhaust gases can be condensed into liquid. However, this approach requires that an air-conditioning system is actually installed in the vehicle, and that it is operated even at times when not necessary for the comfort of vehicle occupants. The latter would undoubtedly result in a very significant wear on the air-condition system and reduced fuel efficiency of the automotive vehicle. Said Andrews 2 and said Zagaja et al. each disclose a method of cooling ICE exhaust gases using a thermo-electric cooler (TEC). While this approach can be effective, TEC is expensive, requires significant amount of electric power to operate, and generates significant amount of heat that must be rejected.
One of the challenges of generating and storing liquid water onboard an automotive vehicle is the potential for freezing in cold weather conditions. Andrews 3 discloses a water source wherein resistance against freezing is obtained by keeping the water source components in a thermal contact with warm components of the ICE. However, Andrews 3 does not disclose which components are thermally connected, or specific means by which such a thermal contact is accomplished, or how temperature control is maintained.
It is well known in the art that when a mixture of gases containing water vapor is compressed above ambient pressure its dew point increases, which means that liquid water condensation can occur at a higher temperature. This phenomenon is actually a hindrance in many compressed air installations. Therefore, various means have been devised to dehumidify compressed air in industrial application. See, for example, Ewing et al. in U.S. Pat. No. 2,077,315 or Alderson et al. in U.S. Pat. No. 3,226,948. Devices and methods for direct extraction of water from air using condensation at above ambient pressure have been disclosed by Spletzer et al. in U.S. Pat. Nos. 6,230,503, 6,360,549, and 6,511,525. However, Spletzer does not show how this approach could be used to extract liquid water from hot ICE exhaust gases on an automotive vehicle under all-weather conditions. In particular, Spletzer does not teach cooling of hot ICE exhaust gages prior to compression, prevention of particulates entering the compressor, operating the compressor from ICE shaft, condensing and collecting liquid water, preventing collected water from freezing, and delivering liquid water to end use stations within an automotive vehicle.
In summary, the prior art does not teach an ICE system with a water source that is operational at all atmospheric conditions, that is robust to freezing conditions, and that is simple and inexpensive to operate. Consequently, there is a great need for new devices and methods for extracting liquid water from ICE exhaust gases. Suitable water source should use very little motive power as not to significantly reduce vehicle mileage, should be capable of operating without human intervention in hot and cold climates and under any weather conditions including freezing conditions, should endure storage under freezing conditions without damage, should be robust to vibrations, and should be inexpensive to manufacture and integrate into automotive vehicles.